The present invention concerns the technical field of mineral fillers, in particular for paper-making applications, and their improvement by suitable treatments in order to improve either the manufacturing process of the paper sheet or its properties.
Such fillers are well known to a specialist in the field and we can quote for example natural calcium carbonate, synthetic or xe2x80x9cprecipitatedxe2x80x9d calcium carbonate (xe2x80x9cPCCxe2x80x9d), and various fillers such as dolomite, mixed fillers based on different carbonates of metals such as calcium joined with magnesium and similar, various fillers such as talc and similar, and mixtures of these fillers, for example mixtures of talc and calcium carbonate, calcium carbonate and kaolin, or mixtures of natural calcium carbonate with aluminium hydroxide, mica or synthetic or natural fibres.
It will also be useful to give details of the process of manufacture of a sheet of paper, board or similar. A specialist in the field will know that a paste (xe2x80x9cpulpxe2x80x9d) is made, essentially comprising fibres (cellulose fibres of natural origin such as from resinous or deciduous wood or of synthetic origin or a mixture of both), a filler as defined above and a suitable proportion of water.
A thick paste or xe2x80x9cthick stockxe2x80x9d is made and then diluted with water to produce a diluted paste or xe2x80x9cthin stockxe2x80x9d. The pulp receives various additives, such as certain polymers, in order to improve the conditions of flocculation and therefore of xe2x80x9cformingxe2x80x9d of the sheet, of water retention and of water drainage under the wire. The aqueous medium containing a fraction of the initial filler, which is drained under vacuum under the wire is known as xe2x80x9cwhite liquorxe2x80x9d. The sheet then undergoes various processes, including an important operation known as coating. It is known that during this coating operation there occur losses of coating color and of coated paper. This coated paper is recycled as a mass filler and is known as xe2x80x9ccoating brokexe2x80x9d.
The invention particularly concerns the treatment, by a combination of one or more medium-strong to strong H3O+ ion-providers in an active gaseous medium, of pigments, of fillers or minerals in aqueous suspension, containing natural carbonate such as natural calcium carbonate or containing any pigment containing natural calcium carbonate in combination with other minerals. It is indeed logical that natural calcium carbonate can be mixed with minerals which are inert with respect to the medium-strong to strong H3O+ ion-providers well known in the paper industry.